No, you cannot. 30-30 is longer and skinnier than the 303 Savage, you could definitely injure yourself. Shoot 303 Savage ammo or put it away.

Now don't get me wrong, I have known people who swear the 303 Savage and the 30-30 are the same thing, and have even fired 30-30 ammo in their old 99s chambered for 303. But the brass is unusable afterwards, and they were only saved by the long throats Savage used on the 303 Savage becasue it was originally loaded with 190 gr bullets.